The embodiments herein relate to methods and compositions for treating a subterranean formation with salt-tolerant cement slurries.
Various methods are known for completing a subterranean formation in order to recover hydrocarbons, natural gas, or other extractable substances from the formation (e.g., open-hole completions, liner completions, cased hole completions, etc.). During many completion operations, a casing is inserted into a drilled well and a cement slurry is pushed through the bottom of the casing and out through an annulus between the outer casing wall and the formation face. The cement slurry then cures in the annular space, thereby forming a sheath of hardened, substantially impermeable cement (a “cement sheath”) that, inter alia, supports and positions the casing in the wellbore and bonds the exterior surface of the casing to the subterranean formation. Among other things, the cement sheath surrounding the casing serves to prevent contamination of non-hydrocarbon zones from contacting the produced hydrocarbons. For example, the cement sheath may keep fresh water zones from becoming contaminated with produced fluids or gases from within the casing. The cement sheath may also prevent unstable formations from caving in, thereby reducing the chance of a stuck drill pipe or a casing collapse. Finally, the cement sheath forms a solid barrier to prevent fluid loss or contamination of production zones. The degree of success of a completion operation (e.g., fracturing and fluid recovery) therefore depends, at least in part, upon the adequate cementing of the wellbore casing.
Salt formations are encountered in many oil-producing regions. Salt formations, particularly those containing, but not limited to, sodium, potassium, calcium and magnesium monovalent and divalent cations (e.g., Na+, K+, Ca+, and Mg+), may interfere with the ability of traditional cement slurries to form a satisfactory cement sheath. The cations from the salt formation may creep into, contaminate, and chemically react with the cement slurry. For example, divalent cations may viscosify (or gel) the cement slurry, altering the setting properties and thus the final mechanical strength of the cement slurry, often resulting in improper zonal isolation and/or casing collapses. Traditional cement slurries are unable to thwart the effects of salt contamination while still maintaining the desired cementing properties. Therefore, a cement slurry composition and a method of preparing said cement slurry that is capable of mitigating or eliminating the gelling effects of salt contamination for use in oil-producing regions with salt formations, without compromising the cement slurry's cementing capabilities (e.g., complete zonal isolation) would be beneficial to one of ordinary skill in the art.